The present invention relates to a method and apparatus for forming a stream of partly overlapping paper sheets or the like. More particularly, the invention relates to improvements in a method and apparatus for converting a first stream of discrete sheets which are spaced apart from each other into a second stream wherein the sheets overlap. Still more particularly, the invention relates to a method and apparatus for converting a first stream of discrete non-overlapping sheets or analogous commodities into a second stream wherein the commodities overlap regardless of whether or not certain commodities of the series of commodities which form the first stream are missing.
It is already known to convert a stream of rapidly moving discrete sheets into a stream of partly overlapping sheets. The apparatus which are utilized for such conversion employ a braking device which decelerates successive foremost sheets of the first stream and a mechanical deflector serving to flex the trailing end of the sheet which is subjected to the braking action so that the oncoming rapidly moving sheet of the first stream can catch up with and partially overlie or underlie the preceding sheet. The locus of deflection of successive braked sheets is ahead of the braking station, and the distance between such locus and the braking station corresponds to or approximates the length of a sheet.
The just described apparatus operate properly as long as the width of clearances between neighboring sheets of the first stream is uniform or deviates only negligibly from a standard width. In the absence of such uniformity of the width of clearances, the trailing portion of a sheet which is being braked can return into the path of the oncoming foremost sheet of the first stream before the foremost sheet advances sufficiently to overlap the preceding (braked) sheet. In other words, when the first stream exhibits a relatively wide gap which is due to the absence of one or more sheets, the just described apparatus are incapable of converting the first stream into a continuous stream of partly overlapping sheets. If the next-following sheet is permitted to strike against the rear edge of the preceding (braked) sheet, the sheets are likely to be deformed and/or otherwise damaged, and one or both sheets are likely to change orientation so as to interfere with orderly processing of sheets which form the second stream. Removal of certain sheets from the first stream is often necessary or desirable, e.g., for the purposes of insepction or to segregate defective sheets. Each such removal results in the formation of a gap in the stream of partly overlapping sheets or in a pileup of sheets at the braking station.
It was already proposed to utilize apparatus wherein the stream of partly overlapping sheets is temporarily arrested in response to detection of a gap in the stream of non-overlapping sheets. Such stoppage of the stream of overlapping sheets serves to enable the foremost sheet of the first stream to catch up with the last sheet of the second stream. The second stream is set in motion when its last sheet is overlapped by the oncoming rapidly advancing sheet of the first stream. The just described mode of operation is not entirely satisfactory, especially when the apparatus is to process sheets at a high speed and/or when the sheets are heavy and bulky (each sheet may constitute a single panel or leaf of paper or other flexible sheet material, or a stack of overlapping sheets, such as a note book, steno pad or the like). The braking and accelerating forces which must be applied to effect repeated stoppage and transport of the second stream are very pronounced and invariably cause extensive wear upon the components of the apparatus. The sheets of the second stream are likely to slip relative to their conveyor or conveyors and to thus change their orientation; this affects the operation of devices which receive the sheets of the second stream. Still further, such apparatus cannot prevent damage to the last sheet of the arrested second stream and/or to the foremost sheet of the first stream unless the deflection of the trailing portion of the last sheet of the second stream is timed with utmost accuracy. Therefore, the just described apparatus can function satisfactorily only as long as the speed of sheets is relatively low, namely, well below the speed which is required in a modern high-speed machine for the processing of paper sheets which are to be assembled into note books or the like.